We fabricated an optically transparent monopole antenna using graphene film and investigated the feasibility of the film as an electrode material for antennas. A low sheet resistance (80 Ω/sq) was attained by stacking the graphene films and carrier doping with an ionic liquid. The optical transmittance of the carrier-doped three-layer stacked graphene film was greater than 90%, enabling it to be embedded in highly transparent objects without altering their landscape. Using the monopole antenna structure with a metal ground plane, we measured the reflection and radiation characteristics of the graphene monopole antenna, excluding the contribution from the power feeding components. The radiation efficiency of the graphene monopole antenna, which was measured by the Wheeler cap method, was determined to be 52.5% at 9.8 GHz. Through the measurements of the graphene monopole antenna, we demonstrated that the carrier-doped three-layer stacked graphene film can be used as an electrode material for optically transparent antennas.
Transparent antennas have attracted much attention because they can meet the demands of the Internet of Things (IoT) and fifth generation (5G) mobile communication technologies. From this point of view, intensive research and development has been carried out to produce materials with high optical transparency and low electrical resistance. Research on graphene transparent antennas is reviewed along with our experimental demonstration. The unique features of graphene as a material for transparent antennas are introduced and compared to the characteristics of metal-based and metal-oxide transparent conductors. The challenges involved in the fabrication of transparent antennas using graphene films grown by chemical vapor deposition (CVD) are described. Fabrication techniques of transparent antennas (transfer and patterning methods) and techniques to decrease the sheet resistance of the graphene films (stacking and doping methods) are described. The performance of the CVD graphene transparent antennas we have fabricated are presented.
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